Unison (properly, not like many random gatherings of voices), fifths, and thirds, in parallel for several consecutive notes, is a very powerful sound

Don't forget the Rock Guitarists 'Power Chords' trick.

'Classically trained' music students are strongly discouraged from doing it when practising their music theory exam study - being heavily marked down - parallel thirds are allowed a bit more than the other two, especially parallel fifths are frowned on.

'F*lk Musos' can do whatever they want - 'whatever feels good'...